1. Field of the Invention
The present invention relates generally to a chain link plate, and more particularly to a link plate for a power transmission chain driven for running while a side edge of the link plate is kept in sliding contact with a shoe surface a chain guide and the like.
2. Description of the Related Art
Conventional power transmission chains generally include a link plate A1 having rectilinear side edges A2, as shown in FIG. 6(a), or a link plate B1 having curvilinear side edges B2 concaved at longitudinal central portions thereof, as shown in FIG. 6(b).
In a conventional power transmission chain C shown in FIG. 7(a), the link plate A1 having a contour shown in FIG. 6(a) is used as both inner and outer plates of the power transmission chain C. The power transmission chain C is trained around a drive sprocket S1 and a driven sprocket S2 for transmitting rotation of the drive sprocket S1 to the driven sprocket S2.
A chain guide X is disposed exteriorly of a loop of the power transmission chain on a tension run side of the power transmission chain C. The chain guide X has a shoe surface G designed for sliding contact with a side edge A2 of each link plates A1 to prevent the tension run of the power transmission chain C from swinging or whipping while the chain C is running.
Similarly, a tensioner Y disposed exteriorly of the chain loop on a slack run side of the power transmission chain C has a tensioner lever R pivotally connected at one end by a pivot pin J, and a tensioner body H urging the other end (distal end) of the tensioner lever R from the back in a direction to force a shoe surface G' of tensioner lever R against the side edges A2 of the link plates A1. The tensioner Y thus constructed operates to remove a sag of the power transmission chain C so that the slack run of the power transmission chain C is prevented from whipping while the chain C is running.
In the conventional power transmission chain C, when the rectilinear side edge A2 of each link plate A1 is in sliding contact with the shoe surface G' curving outward, as shown in FIG. 7(b), the side edge A2 and the shoe surface G' are contacting at one point P. Since the contact point P changes unstably on the side edge A2 as the chain C moves, the contact pressure between the side edge A2 and the shoe surface G' becomes high and thus makes it difficult to form a lubricating oil film between the side edge A2 and the shoe surface G'. Even when a lubricating oil film is formed between the side edge A2 of the link plate A1 and the shoe surface G', such lubricating oil film is likely to be broken or ruptured. Thus, the power transmission chain C while running is subjected to a relatively large running resistance due to break of the lubricating oil film.
When the side edge A2 of the plate A1 is in sliding contact with a flat shoe surface G of the chain guide X, as shown in FIG. 7(c), the side edge A2, due to its rectilinear configuration, engages with the flat shoe surface G over the entire area thereof. This engagement makes it difficult to keep a lubricating oil film between the side edge A2 and the shoe surface G. Additionally, due to a large contact area between the side edge A2 and the shoe surface G, the power transmission chain C while running encounters a large running resistance.
In the case of a power transmission chain having link plates B1 narrowed at longitudinal central portions, as shown in FIG. 6(b), the curvilinear side edge B2 of each link plate B1 comes into sliding contact with the flat shoe surface G at two portions located near opposite longitudinal ends of the side edge B2, as shown in FIG. 8. The link plate B1 having such curvilinear side edge B2 has a smaller contact area relative to the shoe surface G as compared to the link plate A1 having the rectilinear side edge A2 shown in FIG. 6(a). However, due to the narrowed longitudinal central portion of the link plate B1, there is a large space S formed between a concaved central portion of the side edge B2 and the shoe surface G. The large space S cannot retain or hold within it lubricating oil L, tending to cause break of the lubricating oil film at contact points between the side edge B2 and the shoe surface G.